Session 1 - Solar magnetic variability and irradiance over the solar cycle

Conveners: Marc DeRosa (LMSAL), Jesper Schou (MPS)
Monday 29/10, 17:00 - 18:00

Given that both the solar magnetic field and the solar irradiance has been continuously sampled with space-based instruments for almost an entire 22-year solar cycle, what is the relation between these two observables and what conclusions can be drawn from such relations?

Plenary speaker: Kok Leng Yeo (MPS)

Talks

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Monday October 29, 17:00 - 18:00

17:00	Solar irradiance variability and surface magnetism	Yeo, K	Invited Oral
	Kok Leng Yeo, Sami Solanki, Natalie Krivova
	Max Planck Institute for Solar System Research
	The variation in solar irradiance is commonly assumed to be driven by its surface magnetism. Until recently, this assumption could not be verified conclusively as models of solar irradiance variability based on solar surface magnetism have to be calibrated to solar irradiance measurements. Making use of realistic three-dimensional magnetohydrodynamic simulations of the solar atmosphere and state-of-the-art full-disk magnetograms from SDO, we developed a model of total solar irradiance (TSI) that does not require any such calibration. The modelled TSI variability is therefore, unlike preceding models, independent of TSI measurements. The model replicates over 95% of the observed variability over the lifetime of SDO, confirming the relationship to solar surface magnetism and leaving limited scope for alternative drivers of solar irradiance variability (at least over the time scales examined, that is, days to the solar cycle).
17:30	The GOES EUVS Model: New Operational Spectral Irradiances from GOES-R	Thiemann, E	Oral
	Edward M.B. Thiemann[1], Francis G. Eparvier[1], Thomas N. Woods[1], Andrew R. Jones[1], Martin Snow[1], Donald L. Woodraska[1], Janet Machol[2]
	(1) Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, USA (eparvier@colorado.edu), (2) NOAA Space Weather Predictions Center, Boulder, USA
	In order to monitor solar EUV variability, NOAA has included the EUVS Model, an operational (continuous, high time cadence, low latency) EUV irradiance data product as part of its Geostationary Operational Environmental Satellites (GOES) -R series program. The GOES-R satellites are planned to make observations from 2016-2035, providing nearly two decades of real-time continuous EUV irradiance data, and changing the paradigm for the availability and dissemination of spectral EUV irradiance data. The GOES EUVS Model is an operational, real-time, coarse-resolution EUV spectrum which is derived from the 10 calibrated irradiance measurements of the GOES EXIS instruments. The EUVS Model is based on measurements from SORCE/SOLSTICE, TIMED/SEE and SDO/EVE. In particular, the high time cadence measurements from SDO/EVE are used to calibrate the long-term variability from 6-35 nm and short-term variability from 6-106 nm. The model has a 30 second latency and cadence, and spans the wavelength range from 5 nm to 127 nm. Between 5 and 115 nm, the model spectral resolution is 5 nm, and there is a single 10 nm wide bin from 117-127 nm. The model uses the best available measurements to estimate the irradiance in each model bin, and a spectrum can be produced as long as any one of the EUVS channels (A, B or C) are available. The EXIS model decomposes the EUV irradiance into short and long time-scales, specifically, a daily average and some contribution to the daily value at a 30 second cadence. We show that the model uncertainty for daily average irradiances ranges from 1.6 to 5.4 % for the model bins and that model predictions of M-class or greater flares is typically less than 20% for all bins except the 10-15 nm and 95-100 nm bins, which have uncertainties of 68% and 31.8%, respectively.
17:45	Kinetic and Current Helicity of Long-Lived Activity Complexes During Solar Cycle 24	Komm, R	Oral
	Rudolf Komm[1], Sanjay Gosain[1]
	[1]National Solar Observatory, Boulder, CO 80303
	We study long-lived activity complexes during Solar Cycle 24. We focus on the kinetic helicity below the surface determined with ring-diagram analysis applied to full-disk Dopplergrams from SDO/HMI. In addition, we study the current helicity at the solar surface of these activity complexes determined from synoptic vector magnetograms. Current and kinetic helicity of activity complexes follow the hemispheric helicity rule with mainly positive values in the southern hemisphere and negative ones in the northern hemisphere. The locations with the dominant sign of kinetic helicity are more organized than those of secondary sign even if they are not part of an activity complex, while locations with the secondary sign are more fragmented. We will present the latest results.

Posters

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e-Posters

The solar dynamo: Inferences from observations	Cameron, R
Robert Cameron [1]
Max Planck Instute for Solar System Research
We will show that the observed large-scale structure of the poloidal and toroidal magnetic fields, together with the differential rotation and surface meridional flow argue strongly in favour of a Babcock-Leighton dynamo. The cycle-to-cycle variability is consistent with the idea that flux emergence takes place in a turbulent environment, and we will discuss some of the implications of this in the context of the model.
Delayed Babcock-Leighton dynamos with high diffusion.	Fournier, Y
Yori Fournier[1], Rainer Arlt[1], Detlef Elstner[1]
[1]Leibniz Institute for Astrophysics Potsdam (AIP)
The solar dynamo is often attributed to the Babcock-Leighton mechanism in which magnetic flux tubes rise to the surface, turn into poloidal flux loops and eventually contribute to the global poloidal field of the Sun. The rise of the tubes is typically considered instantaneous, and the magnetic flux density at which the mechanism saturates is taken to be a value in equipartition with the convective motions. Such models deliver solar-like solutions only in the advective-dominated regime, requiring magnetic diffusivities significantly lower than the estimates. In this talk, we present delayed Babcock-Leighton dynamos employing rise times and saturation fields obtained from direct numerical simulations of rising magnetic flux tubes. We demonstrate that the non-linear effect due to the temporal non-locality (the delay) leads to exotic solutions which deliver solar-like activity in the diffusive-dominated regime.
The photospheric structure of coronal holes: magnetic elements	Hofmeister, S
Stefan Hofmeister, Dominik Utz, Stephan Heinemann, Astrid Veronig, Manuela Temmer
Institute of Physics, University of Graz, Graz, Austria
Coronal holes attracted recently more attention by the scientific community as they represent the source region for the fast solar wind which is ifself an important ingredient in understanding the space environment and space weather. Nevertheless, our knowledge about the detailed magnetic field structure below coronal holes is quite limited, maybe since such a research would necessarily involve the high atmospheric and photospheric community. In this contribution we would like to bridge this gap and investigate in detail the magnetic field distribution below coronal holes and its relationship to the large-scale coronal hole topology. To do so, we investigate the distribution and properties of photospheric magnetic elements below 106 low and medium latitude coronal holes using SDO/HMI line-of-sight magnetogram data from 2010 to 2016, and relate them to the overall properties of the coronal holes. Since magnetic elements produce clearly visible photospheric structures, they can be well observed and give us valuable insights into the structure of coronal holes. We find that the distribution of the magnetic flux of magnetic elements follows an exponential function. The area and flux of magnetic elements are strongly related to each other by a power law with an exponent of 1.25. The larger magnetic elements are located at the edges of the magnetic network and seem to be the “core” structure of coronal holes. They have lifetimes > 4 days, i.e., longer than the timescale of the supergranulation. Further, they contain up to 50 magnetic bright points as observed by Hinode/SOT in the G-Band, meaning that the large magnetic elements are large clusters of individual magnetic elements. The mean magnetic field density of the overall coronal holes and thus their unbalanced magnetic flux is determined by their percentage coverage with magnetic elements at cc=0.98. Since magnetic elements are the foot points of magnetic funnels and thus the small-scale source regions of high-speed solar wind streams, the dependence of the coverage with magnetic elements on the strength of coronal holes also explains the dependence of the plasma density of high-speed streams near the Sun to the strength of its source coronal hole. The rotation rates of the magnetic elements match the rotation rate of the coronal hole and is surprisingly similar to the differential rotation rate of active regions at low- and medium latitudes, suggesting they are rooted at similar deep layers. This also means that coronal holes do not show an abnormal rotation rate as suggested by various authors. Finally, by projecting the magnetic elements to AIA-171 and 193 filtergrams, we surprisingly find that the magnetic elements are not located in the darkest regions of coronal holes. Therefore, the vertical plasma outflow from magnetic funnels is probably not the primary reason why coronal holes appear as dark patches in EUV images. We conclude that magnetic elements are the basic building blocks of coronal holes which completely determine their magnetic properties.

p-Posters

Study of Ionosphere Variability over equatorial latitude during extreme low solar activity period	Purohit, D
P. K. Purohit & Roshni Atulkar
National Institute of Technical Teachers' Training and Research, Bhopal – 462002, MP, India.
The most important ionospheric parameter total electron content (TEC), derived by analyzing dual frequency signals from the Global Positioning System (GPS) recorded near the Indian equatorial anomaly region, Bengaluru (13.020 N, 77.570E) located within 0 - 15oN of the equatorial anomaly region. We studied Diurnal, monthly, seasonal and annual variability as well as geomagnetic and solar effects on the equatorial ionospheric anomaly (EIA) during the solar minimum period from January 2009 to December 2009. The monthly highest values of TEC are recorded during the March, April and October While the minimum TEC is observed during the month of June, July, December and January. Similarly, It is found that the daily maximum TEC near equatorial anomaly crest yield their maximum values for the period of the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semi-annual variation is seen with two maxima occurring in both spring and autumn. Relative standard deviation for VTEC shows high value at around morning and before sunrise. From the comparison of GPS-TEC with different solar indices, i.e. solar EUV flux(26–34 nm and0.1–50 nm), F10.7 cm solar radio flux and Zurich sunspot number (SSN), it is concluded that the solar index EUV flux is a better controller of GPS-TEC, compared to F10.7 cm and SSN. Keywords: - Total electron contents (TECs); Equatorial ionization anomaly (EIA); Global Positioning System (GPS)
The Sunspot Number recalibration	Lefevre, L
Laure Lefevre[1], Frederic Clette[1], Sophie Mathieu[1,2], Veronique Delouille[1], Rainer von Sachs[2]
[1]Royal Observatory of Belgium,[2]Institut de statistique, biostatistique et sciences actuarielles (ISBA), UCL
We will present here the revision of the Sunspot Numbers undertaken by the whole solar community since 2010 that led to the publication of a new series in 2015 (http://www.sidc.be/silso/newdataset). This well-known index of solar activity had not been revised since its creation by Rudolf Wolf in 1849. For the Sunspot Number, the k scaling coefficients of individual observers were recomputed using new statistical methodologies while the last 50 years were fully recomputed, using all original data from the 270 stations archived by the World Data Center - SILSO in Brussels. For the Sunspot Group Numbers, most corrections rely entirely on original sunspot data, using various approaches. Newly recovered historical sunspot records were added and a critical data selection was applied for the 17th and 18th century, confirming the low solar activity during the Maunder Minimum. The new Sunspot Number series definitely exclude a progressive rise in average solar activity between the Maunder Minimum and an exceptional Grand Maximum in the late 20th century. Residual differences between the Group and Sunspot Numbers over the past 250 years confirm that they reflect different properties of the solar cycle. We also present preliminary results obtained in the context of the VALUSUN (BELSPO-BRAIN) project concerning the statistical modelling of the Sunspot Numbers: this includes constant quality control of the most recent part of the series and the inclusion of significant error bars. We conclude on the implications for solar cycle and Earth climate studies and on important new conventions adopted for the new series: new unit scales, new SN and GN symbols and a new version-tracking scheme implemented at the WDC-SILSO, as a framework open to future improvements of those unique data series.
Measurements of Solar Oblateness during the SDO Mission	Bush, R
R.I. Bush [1], M. Emilio [2], I. Scholl [3], J.R. Kuhn [3], J. Sommers [1]
[1] Stanford University, Stanford, CA, USA [2] Universidade Estadual de Ponta Grossa, Parana, Brazil [3] University of Hawaii, Hilo, HI, USA
Beginning in April 2010, the Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO) spacecraft has been making periodic measurements of the solar shape. The primary observations are 4096 by 4096 pixel full Sun images taken in the continuum of the 617.3 nm Fe I absorption line in 4 linear polarizations. It is necessary to determine the instrument optical distortion in order to extract the solar shape from the full Sun images. This is accomplished during a roll maneuver of the SDO spacecraft in which the spacecraft is rotated 360 degrees around the Sun-spacecraft line while taking a series of images at 32 uniformly spaced roll angles. Measurements of the solar oblateness are typically obtained twice per year, and eighteen roll maneuvers have been performed by the SDO spacecraft to date. Initially these observations were taken in April and October from 2011 to 2014. During the April 2015 roll, however, the spacecraft maneuver was aborted due to a pointing anomaly. This error condition was identified, but subsequent roll maneuvers were shifted to January and July of the following years. The mean equator to pole radius difference over the nine years of observations is 6.0 +/- 1.0 milli-arcseconds. The higher order (hexadecapole) term is consistent with 0. The long term trend of the solar oblateness does not show a correlation with the current solar sunspot cycle. Details of the measurements and trending will be discussed.
Soothing Massage of HMI Magnetic Field Data	Hoeksema, T
J. Todd Hoeksema[1], Yang Liu[1], Xudong Sun[2], Philip Scherrer[1] & the HMI Science Team
[1]Hansen Experimental Physics Laboratory, Stanford University; [2] Institute for Astronomy, University of Hawai'i at Manoa
The Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) has measured solar polarization at six wavelengths across the Fe I 6173 spectral line with one arc second resolution nearly every 90 or 135 seconds since May 2010, and the Stokes parameters are determined every 720 seconds over the full disk. The quality of the filtergrams is remarkably uniform, but the inverted and disambiguated magnetic field values are sometime incorrect or show small systematic variations with time and space. Estimates of the numerical uncertainties are provided for each pixel, but, for some kinds of analysis, having a smoother and more uniform time series can be useful. This report describes methods that can be used to 'massage' the observations to improve consistency and appearance and minimize unwanted variability. Effects considered include issues related to field inversion, disambiguation, instrument sensitivity, optical distortion, and systematic errors due to spacecraft velocity. The resulting 'corrections' typically depend on assumptions about the behavior of the solar magnetic field, so care must be taken when using such results.
On the acoustic mode frequency dependence with solar cycle	Rabello soares, M
M. Cristina Rabello-Soares
Universidade Federal de Minas Gerais
Global modes obtained by applying spherical harmonic decomposition to HMI, MDI and GONG full-disk observations were used. The dependence of solar acoustic mode frequency with solar activity was examined and evidence of a deviation from a linear relation was found indicating a saturation effect at high solar activity. The frequency dependence of frequency differences between the activity minimum and maximum was analyzed.
Tracking of predominant periodicities evolution for PROBA2/LYRA and other long-term solar time series	Wauters, L
Laurence Wauters[1], Marie Dominique[1],Ingolf Dammash[1],Mustapha Meftah
[1]Royal Observatory of Belgium, [2]LATMOS / CNRS / Paris-Saclay University
The periodograms of the PROBA2/LYRA data show predominant periodicities comparable to the ones observed by other solar time series for the same time range. These periodicities have been found to slightly vary over time. Tracking their evolution on a long-term basis aims at identifying which periodicities are related to each other and at determining which physical processes are at their origin. A study has been made on sunspot area, for which several solar cycles of data exist and for which the periodicities are close to the ones found in LYRA (for the same time range). We used framed Lomb-Scargle periodograms to extract the periodicities and check their evolution. Several significant periodicities behave similarly and seem to be harmonically related.